It really depends on what you plan on using the phone for. The Moto Droid is an awesome phone with a ton of potential. You can root it, rom it, and overclock it to your hearts desire. If you are into techy stuff and like tinkering with your gadgets then you should probably stick with the Droid. Keep in mind however, that the Droid is now 9 months old and is reaching it's "End of Life" with Verizon. That doesn't mean it's no longer a good phone, it just means that most likely one more official update or so and that'll be it for a while (I'm guessing at this here). This again goes with if you are a techy person. No official updates doesn't mean much if you're comfortable flashing new roms to it yourself.
Now, on the other side of things. If you are more of a, shall I say, general consumer and just want a phone to work fine and fast out of the box, not have to think about rooting or roms, then you should go with the Droid X because it's the new flagship phone, and support on it will be heavy for a while. I'm sure root will come to the X at some point, but it's very doubtful you'll be able to flash roms to it for a long while, if ever. Both are very good phones and I'm sure will suit you well, you just need to think about what you want overall with your phone.